1. Field of the Invention
The present invention relates to a technique for effecting more reliable picking of a weft during a transition phase in which the number of rotations of a loom is changed, in a multicolor picking loom which changes the number of rotations according to a weft which is selected and picked.
2. Description of the Related Art
In a case where a weft that travels easily and another weft that travels with difficulty are picked in a multicolor picking loom, the loom is usually operated at the number of rotations suitable for the traveling characteristics of the respective wefts in order to improve the productivity of a woven fabric. A weft that travels easily (hereinafter simply referred to as an "easy-to-travel weft") is picked at a large number of rotations. In contrast, a weft that travels with difficulty (hereinafter simply referred to as a "difficult-to-travel weft") requires a traveling time longer than that required by the easy-to-travel weft. Consequently, the difficult-to-travel weft is woven at a number of rotations lower than that at which the easy-to-travel weft is woven. Such an operation is achieved by the technique described in, e.g., Japanese Patent Unexamined Publication No. Hei-5-78955. According to this technique, the maximum allowable number of rotations of a loom, which is determined for each type of weft, is stored in the loom for each picking number, which represents a sequence in which a weft is picked during one picking cycle (a repetition of picking). The maximum allowable number of rotations corresponding to the picking number is output every rotation of the loom by driving a loom motor.
Techniques described in, e.g., Japanese Patent Unexamined Publication No. Sho-62-125047 and Japanese Utility Model Unexamined Publication No. Sho-63-149979, are intended to effect stable picking operations in tandem with changing of the number of rotations of the loom. A picking controller is provided, in advance, with picking conditions; namely, a plurality of picking settings for injection timing and pressure of nozzles. During the operation of the loom, picking conditions corresponding to a signal representing the number of rotations (hereinafter simply as a "number-of-rotations signal") detected are selected from the preset picking conditions, and a weft is picked according to the thus-selected picking conditions.
The above techniques are effected under certain conditions. However, in the event of quick changes in the number of rotations of the loom during a picking phase, optimum picking conditions corresponding to the picking phase are not set, thus causing a picking failure and halting the loom. Given that picking conditions corresponding to a change in the number of rotations of the loom are determined by detection of the number-of-rotations signal, the number of rotations will vary greatly even after setting of the picking conditions. A great discrepancy arises between the number of rotations of the loom at which a weft is actually picked and the number of rotations of the loom achieved when the picking conditions are determined. In practice, the weft cannot be picked under optimum picking conditions. To realize picking of the weft under optimum picking conditions even during the course of changes in the number of rotations of the loom, the change in the number of rotations must be constrained within the extent to which no picking failures arise. Eventually, the number of rotations of the loom can be changed only gradually, with the result that the productivity of a woven fabric is not improved.